Conventionally, control motor-driven cam control valves are disclosed in, for example, Japanese Published Unexamined Utility Model Application No. 61-117971 (reference document 1) and Japanese Published Unexamined Utility Model Application No. 61-117972 (reference document 2).
That is, the cam control valve includes, although not illustrated, a valve casing having a fluid passage and a valve seat, a valve disc that is seated on, and leaves, the valve seat of the valve casing, an elastic body that biases the valve disc in a direction of leaving from the valve seat, a valve stem that is coupled to the valve disc to be supported so as to be freely movable up and down by a top cover of the valve casing, a cam plate that comes into contact with a cam roller provided at an upper end portion of the valve stem to hold down the valve stem, a stepping motor (pulse motor) that drivingly rotates the cam plate, and the like. In the cam control valve, the stepping motor rotates the cam plate to hold down the valve stem via the cam plate, thereby making the valve disc provided at the lower end of the valve stem come into contact with the valve seat.
The stepping motor-driven cam control valve is capable of performing high-accuracy flow rate regulation, which results in excellent practical effects.
Meanwhile, in a cam control valve using a stepping motor, because a cam plate is rotated by a predetermined angle in accordance with a number of pulses supplied to the stepping motor, and a valve stem and a valve disc are slightly displaced by the rotation of the cam plate to regulate a flow rate of fluid, it is necessary to perform zero adjustment so that the valve disc, and the valve stem, are accurately located at a zero position (i.e., a fully open position or a fully closed position) when the valve is fully open or fully closed.
That is, it is necessary to make adjustments so that a minimum radius portion of the cam plate comes into contact with a cam roller, and the valve disc and the valve seat are spaced from each other at a maximum when the valve is fully open. It is also necessary to make adjustments so that a maximum radius portion of the cam plate comes into contact with the cam roller, and the valve disc is seated on the valve seat with an appropriate force when the valve is fully closed.
However, the conventional stepping motor-driven cam control valve described above is not equipped with any adjusting mechanism that adjusts a position of the valve disc, and the like, to the zero position. This brings about the problem that it takes much time and energy for zero adjustment of the valve.
Furthermore, unless a processing accuracy, an assembling accuracy, and the like, of the respective components in the cam control valve are improved, the valve disc may be excessively pressed against the valve seat, or the contact between the valve disc and the valve seat may be insufficient in some cases. As a result, there is a problem in that the valve seat, or the like, of the valve may be damaged, or fluid may be leaked.
In order to solve such problems, the inventors of the present invention, and others, have provided a cam control valve equipped with a height adjusting mechanism by which it is possible to fine adjust an actuator composed of a stepping motor and a cam mechanism in a vertical direction (for example, see Patent Document 3).
With the cam control valve in Patent Document 3, it is easy to fine adjust a vertical height of the actuator because the height adjusting mechanism is provided. However, an adjustable screw of the height adjusting mechanism may be hard to access in some cases. Furthermore, with the cam control valve in Patent Document 3, it is impossible to easily finely adjust force with which the valve disc comes into contact with the valve seat after height adjustment for the actuator.